1) Field of the Invention
The present invention is directed to method for producing low modulus acoustically clear polymeric materials.
2) Description of Prior Art
In general, “acoustically clear” polymeric materials have a low modulus (i.e., stiffness). Examples of these polymeric materials include neoprene, ethylene propylene diene monomer (EPDM) and polyurethane rubbers. Typical applications of these materials encapsulate and protect acoustic projectors and hydrophones from marine environments. In order to function properly in these applications as “acoustic windows”; the polymeric materials need to exhibit a variety of physical properties. The most important of these physical properties provide a close match in density “ρ” and speed of sound “c” with the surrounding medium (for example: seawater). The speed of sound and density tend to be directly proportional to the square root of modulus and inversely proportional to the square root of density. Therefore, “hard” and “stiff’ polymers exhibit poor ρ and c matches with seawater and are not used in applications that require acoustic transparency.
However, the lower modulus materials provide less structural strength and certain applications require a higher degree of protection (than is typically provided by the lower modulus materials) while maintaining acoustically clear properties. To maintain a desired structural strength and integrity; holed or cut-out acoustic windows composed of a different material (e.g., rubber) cannot be used. Thus, a hard, strong and acoustically transparent material is needed. Suitable high modulus, castable polymers that also exhibit an acceptable acoustic impedance match with seawater are also needed.